Also, don't be fooled into thinking that if you learn to ride a dirtbike, you can ride a road bike with confidence. They are a completely different ball game. Dirtbikes are an important foundation when learning to ride, though. Get to the stage where you can do a few things on a dirt bike before even attempting a ride on the road with a road bike.
100% Confident when taking off slowly with the clutch
100% confident when giving the bike heaps and dumping the clutch
Being comfortable with the FRONT brake. Some exercises you can try that are pretty hard, but will teach you a lot are these.
Ride kinda slowly on grass and pull the front brake on. The front end will most likely skip out from underneath you for the first few tries, but once you work out how to keep the bike up while the front wheel slides, increase the throttle until you're sliding the front wheel around, and throwing roost at the same time. You should be able to do this without falling off.
Come into a corner and use just the front brake to slow you down, work out how much brake to use, because if you use too much or too little on the bitumen, you'll end up worse for wear. Do these two things until you're 100% comfortable with the front brake.
Once you are, try to learn a stoppie. Don't be fussed if you can't learn this one properly. It will just give you a better idea of transferring your weight on a bike when necessary.
Ride along at a slow speed, hit the back brake, lean your body to the left and let the back end slide to the right, while countersteering. Pull in the clutch and when the bike has nearly stopped, let it out smoothly and take off. Do this the opposite way, lean to the right and let the back end of the bike slide to the left whilst countersteering. Do this until you can get the bike to slide at a 90 degree angle without putting your feet down.
Clutch wheelies...
Once your confident with all the above (clutch, brakes, body position) you should learn how to do clutch wheelies. Not only do they look cool, but they're an important part of bike control.
Go at a very slow pace, slower than walking, pull in the clutch, give it a bit of a rev and lean back whilst popping the clutch. The wheel will come up in the air a bit. Keep practicing until you can get to the stage where you can give it a handfull and ride on the back wheel for as long as you have room infront of you. You can then learn to change gears while doing it if you want.
This probably isn't necessary at all if you want to ride road bikes, but knowing how to jump brings another element into riding. Using throttle, brakes, clutch and body position to get the bike to be where it needs to be in the air is important (I reckon anyway).
Riding on the dirt will teach you how to read terrain, this is VERY important regardless of where and what you're riding, you'll gradually get faster and better.
Two things to remember though:
Unless you push yourself, you'll grow bored of riding. You need to progress to get that rush that you'll get when you jump on a dirtbike for the first few days.
There are two types of riders, those who have crashed and those who are going to crash. I guarantee if you try the exercises I've outlined for you, you'll stack it. Don't worry, it's part of learning and also can be a bit of a rush, I've had my fair share of stacks, including big ones where my bike has tackled me from about 20 foot up.
Once you've gotten half decent on a dirt bike, all you have to do is change the way you ride on a road bike, and you'll know your way around a bike so it will come naturally to you.